Allow comments in mapping files

README.md

@@ -88,6 +88,7 @@ with `-statsd.add-suffix=false`.
 
 An example mapping configuration with `-statsd.add-suffix=false`:
 
+    # comments are allowed
     test.dispatcher.*.*.*
     name="dispatcher_events_total"
     processor="$1"

mapper.go

@@ -59,6 +59,11 @@ func (m *metricMapper) initFromString(fileContents string) error {
 	for i, line := range lines {
 		line := strings.TrimSpace(line)
 
+		// skip comments
+		if strings.HasPrefix(line, "#") {
+			continue
+		}
+
 		switch state {
 		case SEARCHING:
 			if line == "" {

mapper_test.go

@@ -28,11 +28,14 @@ func TestMetricMapper(t *testing.T) {
 		// Config with several mapping definitions.
 		{
 			config: `
+				# this is a comment
+				# this is another
 				test.dispatcher.*.*.*
 				name="dispatch_events"
 				processor="$1"
 				action="$2"
 				result="$3"
+				# here is a third
 				job="test_dispatcher"
 
 				test.my-dispatch-host01.name.dispatcher.*.*.*